The electrical activity of the heart has been known about since the 18th century and an electrocardiogram (ECG) were first recorded in the late 19th century. Since then, systems to record an ECG have become smaller and more widespread. Wearable technology now allows you to record your own ECG.
You'll usually have an ECG if your doctor or healthcare professional thinks you are having symptoms of:
- a heart attack
- coronary heart disease
- structural heart disease
- arrhythmia (problems with how quickly or regularly your heart beats)
There are some things you can do to help you prepare for an ECG, such as:
- wearing a top that is easy to take on and off
- avoiding body lotions, oils or talcum powder
- Some people may also need to have their chest shaved and cleaned before the test.
Having a standard 12-lead ECG is simple and painless. It usually involves attaching 10 wires to sticky electrode patches on your limbs and chest before performing a 10 second recording while you are lying still.
A standard ECG consists of 12 ‘leads’ (i.e 12 lead ECG) with each lead looking at the electrical activity in different areas of your heart. These are usually displayed in a 3x4 grid with a single continuous ‘lead’ at the bottom serving as a rhythm strip.
The various ‘waves’ on the ECG correspond to different parts of your heart being electrically activated and are called PQRST.
The P wave is the electrical impulse spreading through the top chambers of your heart (atria) and the QRS waves are the electrical impulse spreading through the bottom chambers of your heart (ventricles).
Note there is a slightly delay between the P and QRS waves to allow the atria to finishing emptying, before the ventricles are activated. When the ventricles are activated, they contract and this is when you have a heartbeat.
The T wave occurs as the electrical circuits in your heart reset to their resting state until the next electrical wave arrives.
The size (height or amplitude and width), direction (up or down) and their timing in relation to other components, can help diagnose problems with the electrical activity of the heart as well as any underlying structural abnormalities.